In medical diagnosis applications, the generation of images of a patient based on the detection of ionizing radiation is an important issue. In this context, various imaging methods and systems exist, such as computed tomography (CT), positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Such imaging systems make use of detectors that allow the generation of images based on detected radiation.
As an alternative to scintillator detectors another option is to make use of a detector comprising a semi-conductor material (also called photon counting detectors, as e.g. known from WO 2014/087290 A1). Such a semi-conductor sensors, like cadmium-telluride or CZT for photon-counting direct-conversion detectors as potential candidates for CT, are unstructured contrary to their current-integrating non-spectral scintillator-based counterparts. This, however, may cause an increase in the susceptibility to cross-talk between neighboring detector pixels. This effect is often referred to as charge sharing.
Charge-sharing has two main degrading effects on imaging performance: first, the sharing of charges is stochastic as it depends on the interaction site of the x-ray. This leads to a complete loss of information on the energy carried by the original photon. Second, charge sharing carries signal out of one pixel into a neighbor, hence, will also affect the modulation transfer function of the detection system. For the above two reasons, the suppression and/or correction of charge sharing is highly desirable for semiconductor x-ray detectors.
In Ballabriga et al., A 64 k pixel detector readout chip working in single photon counting mode with improved spectrometric performance, Nucl. Instr. and Meth. A, 2010, a 256×256 channel hybrid pixel detector readout chip working in a single photon counting mode with a new inter-pixel architecture is presented. The chip aims to improve the energy resolution in pixelated detectors by mitigating the effects of charge sharing between channels. Charges are summed in all 2×2 pixel clusters on the chip and a given hit is allocated locally to the pixel summing circuit with the biggest total charge on an event-by-event basis. Each pixel contains also two 12-bit binary counters with programmable depth and overflow control. The chip is configurable such that either the dimensions of each detector pixel match those of one readout pixel or detector pixels are four times greater in area than the readout pixels. In the latter case, event-by-event summing is still possible between the larger pixels. Each pixel has around 1600 transistors and the analog static power consumption is below 15 μW in the charge summing mode and 9 μW in the single pixel mode. The chip has been built in an 8-metal 0.13 μm CMOS technology.
In US 2011/0155918 A1 systems and methods for providing a shared charge in pixelated image detectors are disclosed. One method includes providing a plurality of pixels for a pixelated solid state photon detector in a configuration such that a charge distribution is detected by at least two pixels and obtaining charge information from the at least two pixels. Tire method further includes determining a position of an interaction of the charge distribution with the plurality of pixels based on the obtained charge information.
In WO 2004/021698 A1 a detector arrangement for the conversion of electromagnetic radiation into electrical signals is disclosed. The detector arrangement includes sensitive areas where each sensitive area corresponds to a respective electrical signal, and at least two of the sensitive areas mesh with one another in such a manner that non-overlapping envelopes of the individual meshing sensitive areas also mesh with one another.
In Cunningham et al., Cosmic-ray detector with interdigitated-finger pixels for two-dimensional position information from a single wafer side, 1993, a type of cosmic ray detector for isotopic and energy detection of energetic nuclei is disclosed. Both dimensions of position information are derived from one side of the detector. This simplifies the required readout electronics.
However, there is still a need for improving photon counting detectors with respect to their susceptibility for charge-sharing effects.